Mobile station can transmit uplink data to a base station through a method of using a random access process and a scheduled access process.
In general, when the number of users within a cell is small, the random access process is more effective than the scheduled access process in the aspect or latency and throughput.
When the number of users increases within a cell, the probability of contention in random access increases, thereby abruptly decreasing the efficiency of uplink transmission.
However, if the number of users increases when the coverage is wide such as a cellular network, then centralized control through scheduling is effective.
Though a small-sized cell such as femto-cell is based on cellular technology, random access is effective since the number of users within a cell is small.
Hereinafter, a typical random access process will be described in brief with reference to the accompanying drawings.
FIG. 1 is a view illustrating an uplink resource allocation procedure of a mobile station using a contention-based request scheme.
Referring to FIG. 1, a mobile station transmits a CDMA code randomly selected for a slot that is randomly selected from an area allocated to the bandwidth request in uplink (S110).
If the base station recognizes the CDMA code sent from the mobile station, then the base station allocates resources to which a bandwidth request message is transmitted using a CDMA allocation information element (CDMA_Allocation_IE) (S120).
The mobile station that has received information on uplink resources for transmitting a bandwidth request message transmits the bandwidth request message to the relevant resource area. At this time, the mobile station may use a bandwidth request (BR) header, and the header may include information on a size of the requested bandwidth and the like (S130).
If the bandwidth requested by the mobile station is available, then the base station allocates uplink resources to the mobile terminal (S140).
The mobile station transmits data to the allocated uplink resources (S150).
FIG. 2 is a view illustrating an example of a 3-step random access based bandwidth request process.
The mobile station in a broadband wireless access system may use a 3-step or 5-step random access scheme. The 5-step random access scheme may be used independently from the 3-step random access scheme, and used also as a fall-back mode when the 3-step scheme is failed.
An advanced mobile station (AMS) transmits a bandwidth request preamble sequence and quick access message to a serving advanced base station (S-ABS) in a randomly selected opportunity (S210).
At this time, the quick access message may include a station identifier (ID), which is uplink bandwidth request information, a BR index indicating a bandwidth request size and QoS, and the like.
The base station may transmit a BR ACK A-MAP (advanced MAP) information element to mobile stations in the form of broadcast/multicast (S220).
Furthermore, the base station that has normally received the BR preamble sequence and quick access message allocates uplink resources to each mobile station, and transmits uplink resource allocation information to each mobile station through a UL basic assignment A-MAP information element (UL basic assignment A-MAP IE) (S230). The mobile station may transmit uplink data to the base station through the allocated uplink transmission area. At this time, the mobile station may transmit an additional uplink bandwidth request to the base station at the same time (S240).
FIG. 3 is a view illustrating an example of a 5-step random access based bandwidth request process as a contingency plan for the failure of 3-step.
The mobile station transmits a BR preamble sequence (or BR code), uplink bandwidth request information (station ID), a BR index indicating a request size and QoS, and the like, using a quick access message (S310).
The base station can transmit the receiving status of a BR preamble sequence and quick access message transmitted by each of the mobile stations through a BR ACK A-MAP information element to the mobile stations. However, it is assumed that the BR preamble sequence is normally decoded but the quick access message is failed. Accordingly, the BR ACK A-MAP information element indicates that the BR preamble sequence has been normally received and the quick access message has an error (S320).
The base station that has normally received only the BR preamble sequence transmitted from the mobile station allocates uplink resources for allowing the mobile station to transmit a bandwidth request (BW-REQ) message to the mobile station through a CDMA allocation A-MAP information element (CDMA Allocation A-MAP IE) (S330).
In the step S330, the CDMA A-MAP information element may be transmitted in the grant form for independent BR.
The mobile terminal transmits a BW-REQ message (e.g. independent BR header format) through the allocated area (S340).
The base station that has received the BW-REQ message transmitted by the mobile station allocates uplink resources to the mobile station using an uplink basic assignment A-MAP information element (UL basic assignment A-MAP IE) or a grant message for uplink data transmission (S350).
The mobile station transmits UL data through the located uplink resource area to the base station. At this time, the mobile station can transmit an additional uplink bandwidth request information element at the same time to the base station (S360).
FIG. 3 illustrates a 5-step random access scheme as a contingency plan for the failure of the 3-step random access scheme in FIG. 2. However, a typical 5-step scheme is distinguished from FIG. 3 only in that the mobile station does not send a quick access message in the step S310, and the remaining processes may be used and carried out as they are described in FIG. 3.
As described above, according to a typical random access process, uplink resources are allocated by a request of the mobile station, and uplink data burst transmission should be carried out through the allocated resource area, thereby causing a problem that time is delayed until the uplink data burst transmission.